Electric arc torch



C. C. POTTER ELECTRIC ARC TORCH Feb. 23, 1965 2 Sheets-Sheet 1 Filed Sept. 6, 1962 INVENTOR.

" W W 10 W Feb. 23, 1965 c. c. POTTER 3,171,010

ELECTRIC ARC TORCH Filed Sept. 6, 1962 2 Sheets-Sheet 2 kn a INVHVTOR.

United States Patent 3,171,010 ELECTRIC ARC TORCH Charles C. Potter, White River Junction, Vt., assignor to Thermal Dynamics Corporation, a corporation of New Hampshire Filed Sept. 6, 1962, Ser. No. 221,727 3 Claims. (Cl. 21975) My invention relates to electric arc torches and relates more particularly to a torch of that type in which plasmaforming gases are used for the dual purpose of stabilizing the electric arc and providing the vehicle for heat energy transfer.

One'of the basic methods of introducing gases to a torch is to form a vortex flow into the arc region, the axis of the vortex being along the desirai line of arcing. This method, and a preferred means of practicing it, is described in U.S. Patent No. 3,027,446, issued March 27, 1962, to James A. Browning. Another method employs a longitudinal flow, the gas traveling in essentially straight lines to form a gas sheath along the arc.

Vortex flow, while highly effective in stabilizing an arc and controlling its emanation from the cathode, unfortunately, exhibits certain disadvantages in particular applications. For example, when it is desired that the plasma efliuent be a coherent jet extending a considerable distance from the torch nozzle, vortex flow produces a less persistent jet than does longitudinal flow. This is because the centrifugal forces of the whirling gas tend to produce a diverging cone When leaving the torch nozzle.

These same forces also make it difficult and often impossible to introduce fusible substances into the vortex when an arc torch is used for spraying such substances to form coatings.

My invention provides a method and means for reaping the advantages of the superior arc-stabilizing and cathode-preserving qualities of a vortex type gas flow, while at the same time avoiding the difficulties heretofore discussed.

For a better understanding of my invention and its underlying principles, reference is now made to the following detailed description and drawings, in which like characters denote like parts, and in which:

FIGURES 1 and 2 are simplified cross sectional views of typical arc torches wherein the two types of flow and resulting effluent are compared;

FIGURE 3 illustrates means and nozzle construction to attenuate the vortex flow in accordance with the invention;

FIGURE 4 is a section taken on the lines 4-4 of FIGURE 3;

FIGURE 5 is an alternate form of the construction shown in FIGURE 3;

FIGURE 6 illustrates another method of vortex attenuation;

FIGURE 7 illustrates a torch constructed in accordance with the invention being operated in the transferred mode; and

FIGURE 8 illustrates a torch being used to spray materials by introducing them into the gas stream.

Referring now more particularly to the drawings, in FIGURES 1 and 2 torch anodes 10 form nozzle passages 11. The anodes 10 may be connected to any suitable power source, not shown, and together with cathodes 12 provide the electrical elements between which arcs 13 and 14 are established. These arcs are stabilized by a stream of plasma forming gases illustrated by the vortex flow 15 of FIGURE 1 and the longitudinal flow 16 of FIGURE 2. It should be mentioned here that in either case, and throughout the following discussion the devices See shown may be operated in the nontransferred mode (FIG- URES 1 and 2) or the transferred mode (FIGURE 7).

It will be noted that the efiluent in FIGURE 1 diverges into a cone 17 while the effluent in FIGURE 2 tends to remain in a coherent jet 18. The reason for this is that a strong vortex is desired in the region around and immediately down stream from the cathode. This vortex, however, persists and the whirling gas particles diverge upon leaving the nozzle opening due to their tangential velocities. It has been found that other conditions being comparable, the arc with vortex fiow extends farther down the nozzle as shown, thus resulting in higher possible voltages (and power levels) and more effective heating of the gases. Furthermore, the low pressure core of the vortex tends to improve operating conditions at the cathode, as described in detail in the aforementioned Browning patent.

In FIGURE 3, I show a new form of anode structure in which the end portion of the torch is characterized by a plurality of longitudinal slots 19 which may be formed as by broaching on the inner wall of the nozzle passage. I have found that these slots effectively reduce the whirling component just before the gases leave the torch, and eflluent characteristics approaching those of FIG- URE 2 are thus achieved. I retain essentially all the advantages of vortex flow within the body of the torch, while avoiding the undesirable type of eflluent configuration heretofore associated with strong vortex arc stabilization. I also prefer to reduce the bore diameter as at 20. The central core of hot gases continues in the axial direction while the peripheral gas impinges on the discontinuities produced by the slots, and its tangential velocity is thereby substantially attenuated.

I shown in FIGURE 5, grooves 21 formed spiral fashion as in rifling. I have found that when the rifling grooves 21 are formed in the opposite sense to the rotation of the gases as tangentially introduced further effective reduction of the vortex is realized. I thus produce an eflluent in the desired form while retaining the advantages of the vortex.

Another means for weakening or neutralizing tangential components of gas velocity is illustrated in FIGURE 6. Here I introduce gas tangentially through apertures 22. At this point the gas enters the nozzle in the opposite direction to that employed at the cathode region, where the main gas stabilizing stream enters the torch. Interaction between these two streams reduces or substantially eliminates the vortex beforethe efiluent actually leaves the torch. It should be noted that the secondary flow at 22 may be an inexpensive gas, such as air, and in a typical application need only be in sufiicient pressures and quantities to oppose whatever normal residual vortex is experienced at the nozzle opening.

In FIGURE 7, the torch employing my invention is operating as a cutter, in the transferred mode. Here the work piece 23 forms the anode. It will be appreciated that a narrow persistent jet 18 is especially required to make deep cuts in which the kerf is kept to a minimum. In this case, the are from the cathode 12 to well down the nozzle passage 11 is effectively stabilized by a strong vortex with all the advantages previously discussed. Yet before leaving the torch body, this vortex is effectively reduced as shown and taught herein, thereby permitting an arc-gas efiluent to assume a form most effective for cutting.

Another common use of arc torches is in the spraying of materials, particularly exotic substances and alloys to form protective coatings on a wide variety of objects. When substances are introduced in regions where vortex forces are present difficulties are experienced. It is essential that the material to be sprayed penetrate the outer, relatively cool gaseous sheath. Straight gas flows generally permit this action. Vortex flows, however, tend to throw the material to the periphery thus making entry into the hot core region extremely difiicult. ing the whirl intensity by any of the methods taught herein, and by introducing the material at the appropriate point, etlective introduction of sprayable substances is achieved. This is shown in FIGURE 8, where, by Way of example, I use slots 19 as hereinbefore described and introduce the desired material (which may be in pow dered form through the duct 24. The are, itself, in the torch of FIGURE 8, thus is controlled by an initially strong vortex of gas, yet materials may be introduced under substantially the same desirable conditions experienced in torches employing straight gas fiow along the entire arc path.

While I have explained a novel method of torch operation and illustrated several embodiments of my invention, variations within the spirit and scope of the following claims may occur to persons skilled in this art.

I claim:

1. In an electric arc torch, at least one electrode, an arc passage extending from said electrode, and terminating in a nozzle opening, means for establishing an are from said electrode, into said passage, means for intro- By reducl ducing arc stabilizing gas tangentially into said passage in the region of said electrode to form a vortex, and means for introducing tangentially a second gas at the nozzle region of'said passage in a direction opposite in sense to said vortex.

2. In an electric arc torch having at least one electrode and an arc passage, means for striking and maintaining an are from said electrode into said passage, means for introducing gas tangentially to stabilize said arc within said passage with a vortex flow around said arc, and means for attenuating the tangential velocity of said gas at the exit region of said passage comprising a plurality of longitudinal slots formed on the inner wall of said passage.

3. An arc torch according to claim 2 in which said slots are formed in spiral fashion on the inner wall of said are passage.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,088'11 /61 Ducatietal 219-75 2,862,099 11/58 Gage 21944 Y 3,082,314 3/63 Arata et al. 21945 RICHARD M. WOOD, Primary Examiner. 

1. IN AN ELECTRIC ARC TORCH, AT LEAST ONE ELECTRODE, AN ARC PASSAGE EXTENDING FROM SAID ELECTRODE, AND TERMINATING IN A NOZZLE OPENING, MEANS FOR ESTABLISHING AN ARC FROM SAID ELECTRODE, INTO SAID PASSAGE, MEANS FOR INTRODUCING ARC STABILIZING GAS TANGENTIALLY INTO SAID PASSAGE IN THE REGION OF SAID ELECTRODE TO FORM A VORTEX, AND MEANS FOR INTRODUCING TANGENTIALLY A SECOND GAS AT THE NOZZLE REGION OF SAID PASSAGE IN A DIRECTION OPPOSITE IN SENSE TO SAID VORTEX. 